Based on structure-activity data from these and other laboratories and in collaboration with Dr. W.H. Sawyer, Dept. Pharmacology, College of Physicians & Surgeons, Columbia University, 630 West 168th Street, New York, N.Y. 10032, studies are underway which we hope will lead to the accomplishment of the following objectives. 1) To continue the study of the structural modifications of arginine vasopressin (AVP) which regulate a) antidiuretic activity, b) antidiuretic specificity and c) protracted antidiuresis. 2) To design and synthesize a selectively acting potent oxytocic agent which is devoid of antidiuretic activity. 3) To synthesize (4-homoserine)-oxytocin. 4) To design and synthesize an antagonist to the oxytocic response of oxytocin. 5) To synthesize an antagonist to the pressor response to AVP. 6) To synthesize an antagonist to the antidiuretic response of AVP. 7) To design and synthesize selectively acting regional vasopressor agents. 8) To continue to supply other investigators with samples of synthetic peptides.